Patent document 1 describe a prior art example of an exhaust gas turbine supercharger (hereinafter, simply referred to as the supercharger) and a turbine housing.
As illustrated in FIG. 15, a turbine housing 601 described in patent document 1 includes an outer shell and an inner shell arranged between a first flange 604, which is connected to a bearing housing of a supercharger, and a second flange 605, which forms an exhaust gas outlet the supercharger. The shells form a double-tube structure.
The outer shell includes a first shell member 610, which is coupled to an outer circumferential surface of the first flange 604, and a second shell member 620, which is coupled to the second flange 605. The shell members 610 and 620 are formed by pressing metal sheets. The shell members 610 and 620 are joined with each other in a lap joint.
The inner shell includes a third shell member 630 coupled to an inner circumferential surface of the first flange 604 and a fourth shell member 640 coupled to an inner circumferential surface of the second shell member 620. The shell members 630 and 640 are also formed by pressing metal sheets. The shell members 630 and 640 are basically joined with each other in a lap joint. More specifically, an inner circumferential surface of a distal end portion 631 of the third shell member 630 and an outer circumferential surface of a basal end portion 641 of the fourth shell member 640 are joined with each other.
As illustrated in FIG. 16, the inner shell includes a tongue portion 650. The tongue portion 650 divides the inner shell into a scroll compartment 608 and an inlet port 607, which draws exhaust gas into the turbine housing 601. As described above, the shell members 630 and 640 are joined with each other in a lap joint at region R, which is indicated by an arrow in FIG. 16. The tongue portion 650 is formed by joining the shell members 630 and 640 as a flare joint.
As illustrated in FIG. 17, the third shell member 630 includes an abutment portion 632 protruding toward a distal side, and the fourth shell member 640 has an abutment portion 642 protruding toward a basal side. The abutment portions 632 and 642 abut against each other and thereby flare joined. The joined part of the abutment portions 632 and 642 form the tongue portion 650.
The turbine housing is thinner than a turbine housing that is metal cast. Thus, the heat capacity of the turbine housing is reduced. As a result, heat does not escape form the exhaust gas that passes through the turbine housing. This effectively heats a catalyst device arranged at a downstream side of the supercharger to purify the exhaust gas.